The present invention relates to a self-drilling and thread-forming connecting element, in particular to a screw having a threaded shank and a drilling point at the end for the chip-forming drilling of a core hole for the threaded shank.
Such screws are known, which drill a core hole themselves in the respective material with a chip-forming action by means of their drilling point, and the screw is subsequently screwed into this core hole with the threaded shank like a sheet-metal screw. In the process, a corresponding internal thread forms automatically. To this end, the diameter of the core hole is designed to be correspondingly smaller in adaptation to the design of the thread on the threaded shank, so that a thread can be formed automatically in the core hole.
The object of the invention is to provide such a connecting element in which the drilling behavior, in particular the initial spot drilling during the drilling of the core hole, is improved.
According to the invention, this is achieved with the drilling point designed as a step drill having at least two drilling steps with different diameters. By this design, according to the invention, the first drilling step, which has a drilling point at the end, can be designed with regard to its cutting geometry specifically for good spot-drilling behavior, whereas the second axially adjoining drilling step serves to continuously drill out the core hole and can have a cutting geometry specifically designed for this purpose. Thus different cutting angles may be provided, preferably the cutting angle of the first drilling step, in order to ensure good spot-drilling behavior, may be designed to be smaller (more acute) than the cutting angle of the second drilling step.
As a result, the connecting element according to the invention is also especially well suited for direct drilling and screwing into sheet-metal materials by virtue of the fact that the sheet rolling skin, which as a rule is relatively hard or tough, can be destroyed by the first step.
The invention is to be explained in more detail with reference to a preferred exemplary embodiment shown in the drawing. In the drawing, the single figure shows the point-side end section of a connecting element according to the invention.